The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to an isolated transducer portion within a magnetic head for improved within-wafer chemical mechanical planarization (CMP).
In a magnetic data storage and retrieval system, a thin-film transducing head generally includes a transducer, a substrate upon which the transducer is built, and an overcoat deposited over the transducer. The transducer typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving that magnetically-encoded information from the magnetic media. The reader portion typically consists of a bottom shield, a top shield, and a giant magnetoresistive (GMR) sensor positioned between the bottom and top shields.
The writer portion typically consists of top and bottom poles, which are separated from each other at the air bearing surface of the writer by a gap layer, and which are connected to each other at a region distal from the air bearing surface by a back gap closer or back via. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers, or a writer core. The writer portion and the reader portion are often arranged in a merged-configuration in which a shared pole serves as both the top shield in the reader portion and the bottom pole in the writer portion.
In the fabrication of magnetic transducing heads, numerous read-write heads are simultaneously constructed, layer by layer, on a single wafer. The wafer is later divided by slicing the wafer into individual read-write heads. The read-write head is built from multiple dielectric or metal layers, which are applied to the wafer surface. The reader includes the bottom and top shields along with multiple, thinner layers. The writer includes the top pole, bottom pole, and coil (single-turn or multi-turn) which is situated near a gap between the top and bottom poles. In addition, electrical leads (usually made of copper) are added to connect the magnetic head to other components.
Multiple features of the read-write head, including but not limited to the shields, poles, coils and electrical leads (commonly referred to as copper studs), require CMP in order to achieve the degree of planarity required to produce magnetic heads which read and write at high areal densities. Two general methods exist for forming and planarizing such features in magnetic heads. One method, known as a damascene process, etches a pattern into a planar, dielectric layer and then fills the pattern with metal. Excess metal is applied over a top surface of the dielectric layer. The excess metal is removed by CMP until the dielectric is re-exposed and the patterned metal surface remains. The second method requires that first, the metal feature be applied to a relatively planar water surface. The metal is patterned via etching, photolithography, milling, and/or methods to form the head features. A dielectric layer is deposited on top of the metal head features so as to cover the features. The oxide coating the top of the head feature is removed via CMP to expose the metal below.
In the field of magnetic heads, the masks of certain planarized layers of the magnetic head have areas of non-uniform pattern density. The non-uniform pattern density of these layers ultimately results in poor post-CMP within-wafer uniformity, however, immediately the non-uniform pattern desnity of the layers results in poor post-CMP within-head uniformity. Poor post-CMP uniformity can impact reader-writer spacing and thermal expansion effects within the head. As the layer planarization (i.e. polishing) takes place, if the density of the head feature layer is not uniform, overpolishing, or dishing, of some of the head features or of the material surrounding the features occurs. The overpolishing results in a thickness variation of the head features across the wafer. Thickness variation impacts the number of read-write heads that perform well across the wafer's surface.
The magnetic head feature densities of the layer in the area to be planarized are typically non-uniform. Thus, when the layer is planarized, valleys in the top surface of the layer result from overpolishing. Because there is less support in the layer areas where the head features are not formed, the material is removed at a faster removal rate, which results in dishing. It is important that the layers of the magnetic head be planar after polishing, however, problems such as dishing occur causing a nonplanar surface. The uneven, or non-uniform, surface impacts reader-writer spacing and performance, and has thermal expansion effects on the magnetic head.
In the semiconductor industry, dummy features isolated from the electrical or magnetic circuits are added to the semiconductor substrate in the wafer build process to improve the post-CMP uniformity. A magnetic head is needed in the art which improves the CMP uniformity of the head features when they are planarized at the wafer level.